In recent years, in the field of iron and steel, for example, a process of continuous casting a thin strip-like slab, hot rolling and heat treating using a device for continuously casting a thin strip-like slab, a hot rolling machine, a heat-treating furnace and the like provided in sequence has been adopted for the production of steel strips from the viewpoint of improving the productivity by the elimination of steps, reduction in cost of installation and basic cost of fuel and the like.
The development of a twin-roll type continuous casting method using two rolls, as disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 63-224846, has led to the practical use of the process of continuous casting/hot rolling/heat treating. In the process of continuous casting of a thin strip-like slab/hot rolling/heat treating process, for example, a molten steel is poured into between two rolls and directly cast in a continuous manner into a thin strip-like slab having a thickness of 2 to 6 mm, and the thin strip-like slab is hot-rolled and heat-treated to prepare a strip which is then coiled by means of a coiler to prepare a coiled, hot-rolled coil.
An iron oxide scale is generally present on the surface of the hot-rolled coil prepared by the above process, and the shape of both side edge portions of the coil is uneven. For this reason, before machining the hot-rolled strip, the strip should be treated by using a pickling device for removing the scale and a trimmer for trimming both side edge portions of the strip.
A conventional method used for this purpose comprises passing a coiled, hot-rolled coil, having a thickness of 2 to 6 mm, through a pickling device provided in a separate line to remove a scale present on the surface of the coil, cold-rolling the pickled strip to a thickness of 0.2 to 3 mm and coiling the cold-rolled strip to deliver the strip as a cold-rolled coil. In the production of a cold-rolled coil by the above conventional method, however, two steps, i.e., pickling and cold rolling, should be additionally provided in a separate line, posing problems such as increased cost of installation and basic cost of heat, lowered productivity and the like.
As described above, in recent years, the practical use of the twin-roll type continuous casting method has made it possible to continuously cast a thin strip-like slab having a thickness of 2 to 6 mm which is then hot-rolled to a strip having a thickness of not more than 2 mm. This has enabled the step of cold rolling to be eliminated. Since, however, hot rolling increases the surface area of the strip, there is an ever-increasing demand for an improvement in efficiency of the steps of pickling and trimming.
On the other hand, when the step of pickling and the step of trimming are provided in series with the continuous casting/hot rolling/heat treatment process, the whole line must be ceased (or stopped) for repair or maintenance in any one step or for other reasons, resulting in lowered productivity. For this reason, it is necessary to construct the production apparatus in such a manner that the process of continuous casting of a thin strip-like slab/hot rolling/heat treatment and the steps of pickling and trimming can be performed separately from each other.
An object of the present invention is to provide an apparatus which can efficiently produce a product, corresponding to a cold-rolled product, from a continuously cast, thin, strip-like slab.
Another object of the present invention is to provide a production apparatus which, in the production of a product corresponding to a cold-rolled product, from the thin strip-like slab, enables a reduction in production cost, shortening of the period for delivery, reduction in quantity of material in progress between steps and the like.
A further object of the present invention is to provide a production apparatus which has the step of pickling and the step of trimming provided in a process of continuous casting of a thin strip-like slab/hot rolling/heat treatment so as to be operated in rapid response to the change of steps.
A yet further object of the present invention is to provide a process for producing a steel product, corresponding to a cold-rolled product, from the above thin strip-like slab.